96 Mr EdiiiQiidston on the Kittkvake, ^c. 
and maintained, as long as any of their descendants remain to 
enjoy it ; and that not until, from the multiplication of the in- 
dividuals of the tribe, their abodes become too circumscribed, 
or until they are forcibly dispossessed of them, do they go in 
quest of a new residence. 
Amongst those families and species, where depredations can 
proceed only to a certain extent, and which have for some years 
reached their height, the numbers that annually arrive to breed 
are usually observed to be nearly the same ; they are generally, 
I believe, greater the year succeeding one favourable for incu- 
bation, and when the young have been remarked to be very 
numerous. 
With regard to those, on the contrary, that are hardly ever 
suffered to rear their young, progressive diminution annually 
takes place. Yet, although repeatedly disturbed, they do not 
quit the scenes of their former domestic happiness, but regular- 
ly, and ineffectually, attempt to renew it, till at length, each 
dropping off by '’age or accident, the family becomes extinct. 
It is interesting to observe the few that remain, still linger- 
ing over their ancient haunts, even after their nests have been 
repeatedly pillaged, and the season for renewing them gone past, 
and zealously endeavouring to defend them from intruders, or 
by their restless movements, and anxious screams, reproaching 
those whom their threats or assaults were unable to expel. 
If they were not under the operation of this powerful and 
imperative law of instinct, why should they pertinaciously cling 
to particular spots, where they are regularly persecuted and 
prevented from breeding, and not seek an asylum in other situ- 
ations unoccupied and unmolested, or retire to comparatively 
protected ones, in the. vicinity "of individuals of their own species, 
with hardly a hill intervening ? If I mistake not, this remark 
extends to herons, rooks, and black-headed gulls ; and though 
some exceptions should exist, the general observation will have 
its advantage. 
I have had occasion peculiarly to verify it, in what has be- 
fallen some migratory birds, that breed in situations easily acces- 
sible. The lesser mews, and terns, and oyster-catcher, for in- 
stance, that breed in flat, exposed situations, near the shores ; 
the curlew and Arctic gull, that breed on the' heaths, have be- 
